For many years it has been general practice to utilize bottles which are sealed by means of the so-called crown closure to package products which effect a positive pressure in the bottles. Exemplary of such products are carbonated beverages such as beer. The crown closure is commonly made of tinplate and its fluted skirt is engaged under a peripheral rib which extends around the neck of the bottle in close proximity to its mouth.
The crown closure suffers from two defects, namely, it requires a special tool to remove it from the bottle and it cannot be used to reclose the bottle. In recent years, non-returnable bottles have come into more general use and these have been adopted for some carbonated beverages. When non-returnable bottles are adopted, it is practicable to adopt the most convenient form of closure consistent with economy in price. The most widely employed form of non-returnable bottle system for carbonated beverages has employed a bottle with an externally screwthreaded neck, having a cylindrical sealing surface between the top of the bottle and the start of the thread. With this bottle, there has been employed a closure in the form of an aluminum shell having a gasket covering the inner surface of the top of the shell which forms a sealing liner. The diameter of the skirt of the closure shell is sufficiently large to fit over the thread on the bottle neck at the maximum size allowed by the range of tolerances set out in the specification of the neck finish of the bottle. The skirt of this shell is deformed by a threadrolling operation carried out in known way to bring it into engagement with the thread on the bottle neck.
While such aluminum closures have received wide acceptance, there is an economic problem due to the high cost of aluminum. Aluminum's high cost is directly proportional to the ever-rising high cost of energy as aluminum production is energy intensive.
A highly promising alternative to the use of aluminum closures is the use of closures made of thermoplastic material. Such materials are becoming more and more economically favorable when compared to aluminum. Exemplary of such closures is the one shown in U.S. Pat. No. 3,067,900. As desirable as it may be to use thermoplastic material, there is one serious drawback, i.e., the tendency of thermoplastic closures to lose their seal as positive pressure builds in the bottle. Since the seal is made by the closure making sealing contact with the bottle, the loss of seal is generally due to the closure flexing, as the pressure builds, resulting in the closure structure being distorted and pulled away from the bottle. To prevent flexing, it is possible to select a very rigid thermoplastic material. However, the seal sought to be obtained when using such materials is not always initially achieved as the rigidity of the material will not allow the sealing configuration to follow structural variations which are commonly present on the bottles. Also such rigid materials are often very expensive. Less expensive materials could be used if the flexing portion of the closure was made thicker to achieve the rigidity sought. But, as is obvious, the cost of such a thicker closure rises in direct proportion to the amount of material used and renders such closures commercially unacceptable.
With the economic realities in mind, it would be highly desirable to redesign the thinner commercial closures used today so that the flexing phenomena will not cause loss of seal but rather will be utilized to increase the fidelity of seal as internal container pressures build.
Therefore, it is an object of this invention to provide an inexpensive thermoplastic closure which is capable of maintaining a seal in response to a positive pressure in a container such as a bottle